An expanded definition of acute respiratory distress syndrome: Challenging the status quo.

Although the Berlin definition of acute respiratory distress syndrome (ARDS), 2012 has been widely used in clinical practice, issues have occasionally been raised regarding various criteria since it was proposed. High-flow nasal oxygen (HFNO) is widely used for effective respiratory support in acute respiratory failure. As patients who do not require ventilation but meet the Berlin criteria have similar characteristics to those with ARDS, the definition of ARDS may be broadened to include patients receiving HFNO. As the PaO2/FiO2 under-recognizes the diagnosis of ARDS, a SpO2/FiO2 value of ≤315 may be considered instead of a PaO2/FiO2 value of ≤300 for diagnosing the condition in resource-constrained settings. In this context, patients with severe COVID-19 always meet other criteria for ARDS except for 7-day acute onset. Therefore, the timeframe for the onset of ARDS may be extended to up to 14 days. An expanded definition of ARDS may allow early identification of patients with less severe diseases and facilitate testing and application of new therapies in patients with a high risk of poor outcomes. Here, we discuss the major controversies regarding the extension of the ARDS definition with a view to improving clinical implementation and patient outcomes.

Efficacy of steroid pulse therapy for miliary tuberculosis complicated by acute respiratory distress syndrome.

Introduction: Acute respiratory distress syndrome (ARDS) is considered a poor prognostic factor for miliary tuberculosis (MTB), but little is known about the effectiveness of steroid pulse therapy for MTB complicated by ARDS. Patients and methods: Medical records were used to retrospectively investigate the prognosis and clinical information of 13 patients diagnosed with MTB complicated by ARDS among 68 patients diagnosed with MTB at our hospital between January 1994 and October 2016. None of the patients had multidrug resistant tuberculosis (TB). MTB was diagnosed by 1 radiologist and 2 respiratory physicians based on the observation of randomly distributed, uniformly sized diffuse bilateral nodules on chest computed tomography and the detection of mycobacterium TB from clinical specimens. ARDS was diagnosed based on the Berlin definition of ARDS. The effect of steroid pulse therapy on death within 3 months of hospitalization was examined using Cox proportional hazards models. Variables were selected by the stepwise method (variable reduction method). Results: Six of 8 patients with MTB complicated by ARDS were alive 3 months after hospitalization in the steroid pulse therapy group, whereas only 1 of 5 patients was alive in the non-steroid pulse therapy group. Analysis of factors related to the survival of patients with MTB complicated by ARDS revealed that steroid pulse therapy was the strong prognostic factor (hazard ratio = 0.136 (95 % CI: 0.023-0.815)). Conclusion: Our findings suggest that steroid pulse therapy improves the short-term prognosis of patients with MTB complicated by ARDS.

Effects of changes in inspired oxygen fraction on urinary oxygen tension measurements.

BACKGROUND: Continuous measurement of urinary PO2 (PuO2) is being applied to indirectly monitor renal medullary PO2. However, when applied to critically ill patients with shock, its measurement may be affected by changes in FiO2 and PaO2 and potential associated O2 diffusion between urine and ureteric or bladder tissue. We aimed to investigate PuO2 measurements in septic shock patients with a fiberoptic luminescence optode inserted into the urinary catheter lumen in relation to episodes of FiO2 change. We also evaluated medullary and urinary oxygen tension values in Merino ewes at two different FiO2 levels. RESULTS: In 10 human patients, there were 32 FiO2 decreases and 31 increases in FiO2. Median pre-decrease FiO2 was 0.36 [0.30, 0.39] and median post-decrease FiO2 was 0.30 [0.23, 0.30], p = 0.006. PaO2 levels decreased from 83 mmHg [77, 94] to 72 [62, 80] mmHg, p = 0.009. However, PuO2 was 23.2 mmHg [20.5, 29.0] before and 24.2 mmHg [20.6, 26.3] after the intervention (p = 0.56). The median pre-increase FiO2 was 0.30 [0.21, 0.30] and median post-increase FiO2 was 0.35 [0.30, 0.40], p = 0.008. PaO2 levels increased from 64 mmHg [58, 72 mmHg] to 71 mmHg [70, 100], p = 0.04. However, PuO2 was 25.0 mmHg [IQR: 20.7, 26.8] before and 24.3 mmHg [IQR: 20.7, 26.3] after the intervention (p = 0.65). A mixed linear regression model showed a weak correlation between the variation in PaO2 and the variation in PuO2 values. In 9 Merino ewes, when comparing oxygen tension levels between FiO2 of 0.21 and 0.40, medullary values did not differ (25.1 ± 13.4 mmHg vs. 27.9 ± 15.4 mmHg, respectively, p = 0.6766) and this was similar to urinary oxygen values (27.1 ± 6.17 mmHg vs. 29.7 ± 4.41 mmHg, respectively, p = 0.3192). CONCLUSIONS: Changes in FiO2 and PaO2 within the context of usual care did not affect PuO2. Our findings were supported by experimental data and suggest that PuO2 can be used as biomarker of medullary oxygenation irrespective of FiO2.

Anterior hilum anastomosis versus posterior hilum anastomosis in a mouse lung transplantation model.

Objectives: The mouse orthotopic lung transplantation (LTx) model is of enormous research value in lung transplantation. This study compares 2 anastomotic methods (anterior and posterior hilum anastomosis) of mouse LTx in term of difficulty, operation time, and postoperative effects. Methods: Twenty mice received LTx with slipknots for anterior hilum anastomosis (AH group), and 28 received LTx with a microvessel clip for posterior hilum anastomosis (PH group), all by a single surgeon. The operation time was recorded and the grafts were evaluated 24 hours after surgery. Results: The success rates in the recipient animals were 85% (17/20) in AH group and 89% (25/28) in PH group (P > .05). The recipient operation time and back table time in AH group were longer than those in PH group (52.8 ± 5.0 vs 47.3 ± 5.7 minutes, 27.8 ± 3.9 vs 25.3 ± 2.8 minutes, P < .05), but the warm ischemia time did not differ significantly (13.1 ± 2.1 vs 12.2 ± 2.6 minutes, P = .258), meaning that the time discrepancies predominantly originated from the hilum treatment. In AH group, 2 cases failed due to pulmonary venous thrombosis and atelectasis respectively at 24 hours after LTx, but none failed in PH group. No significant difference was observed in the postoperative performance of the successful recipients (thoracic radiographs, macroscopic appearance, oxygenation index, pulmonary compliance, pathologic changes) between the 2 groups. Conclusions: Compared with anterior hilar anastomosis, posterior hilum anastomosis with a microvessel clip is less complicated and less time-consuming in the management of hilar structures and causes fewer postoperative complications.

Correlation between brain tissue oxygen tension and regional cerebral oximetry in uninjured human brain under conditions of changing ventilation strategy.

Controversy surrounds regional cerebral oximetry (rSO2) because extracranial contamination and unmeasured changes in cerebral arterial:venous ratio confound readings. Correlation of rSO2 with brain tissue oxygen (PbrO2), a "gold standard" for cerebral oxygenation, could help resolve this controversy but PbrO2 measurement is highly invasive. This was a prospective cohort study. The primary aim was to evaluate correlation between PbrO2 and rSO2 and the secondary aim was to investigate the relationship between changing ventilation regimens and measurement of PbrO2 and rSO2. Patients scheduled for elective removal of cerebral metastases were anesthetized with propofol and remifentanil, targeted to a BIS range 40-60. rSO2 was measured using the INVOS 5100B monitor and PbrO2 using the Licox brain monitoring system. The Licox probe was placed into an area of normal brain within the tumor excision corridor. FiO2 and minute ventilation were sequentially adjusted to achieve two set points: (1) FiO2 0.3 and paCO2 30 mmHg, (2) FiO2 1.0 and paCO2 40 mmHg. PbrO2 and rSO2 were recorded at each. Nine participants were included in the final analysis, which showed a positive Spearman's correlation (r = 0.50, p = 0.036) between PbrO2 and rSO2. From set point 1 to set point 2, PbrO2 increased from median 6.0, IQR 4.0-11.3 to median 22.5, IQR 9.8-43.6, p = 0.015; rSO2 increased from median 68.0, IQR 62.5-80.5 to median 83.0, IQR 74.0-90.0, p = 0.047. Correlation between PbrO2 and rSO2 is evident. Increasing FiO2 and PaCO2 results in significant increases in cerebral oxygenation measured by both monitors.

High-flow nasal cannula therapy, factors affecting effective inspired oxygen fraction: an experimental adult bench model.

Oxygenation through High Flow Delivery Systems (HFO) is described as capable of delivering accurate FiO2. Meanwhile, peak inspiratory flow [Formula: see text] ) of patients with acute hypoxemic respiratory failure can reach up to 120 L/min, largely exceeding HFO flow. Currently, very few data on the reliability of HFO devices at these high [Formula: see text] are available. We sought to evaluate factors affecting oxygenation while using HFO systems at high [Formula: see text] in a bench study. Spontaneous breathing was generated with a mechanical test lung connected to a mechanical ventilator Servo-i®, set to volume control mode. Gas flow from a HFO device was delivered to the test lung. The influence on effective inspired oxygen fraction of three parameters (FiO2 0.6, 0.8, and 1, [Formula: see text] from 28 to 98.1 L/min, and HFO Gas Flows from 40 to 60 L/min) were analyzed and are reported. The present bench study demonstrates that during HFO treatment, measured FiO2 in the lung does not equal set FiO2 on the device. The substance of this variation (ΔFiO2) is tightly correlated to [Formula: see text] (Pearson's coefficient of 0.94, p-value < 0.001). Additionally, set FiO2 and Flow at HFO device appear to significatively affect ΔFiO2 as well (p-values < 0.001, adjusted to [Formula: see text] ). The result of multivariate linear regression indicates predictors ([Formula: see text] , Flow and set FiO2) to explain 92% of the variance of delta FiO2 through K-Fold Cross Validation. Moreover, adjunction of a dead space in the breathing circuit significantly decreased ΔFiO2 (p < 0.01). The present bench study did expose a weakness of HFO devices in reliability of delivering accurate FIO2 at high [Formula: see text] as well as, to a lesser extent, at [Formula: see text] below equivalent set HFO Flows. Moreover, set HFO flow and set FIO2 did influence the variability of effective inspired oxygen fraction. The adjunction of a dead space in the experimental set-up significantly amended this variability and should thus be further studied in order to improve success rate of HFO therapy.

Effect of different inspired fractions of oxygen on F-shunt and arterial partial pressure of oxygen in isoflurane-anaesthetized and mechanically ventilated Shetland ponies.

OBJECTIVE: To determine the effect of fraction of inspired oxygen (FiO2) on intrapulmonary shunt fraction as measured by F-shunt in ponies during isoflurane anaesthesia. STUDY DESIGN: Prospective, randomized clinical study. ANIMALS: A group of 23 adult Shetland ponies undergoing a total of 32 anaesthetic procedures. METHODS: Ponies were premedicated intravenously (IV) with detomidine (0.01 mg kg-1) and either morphine (0.1 mg kg-1) or butorphanol (0.02 mg kg-1). Anaesthesia was induced with ketamine (2.2 mg kg-1) and midazolam (0.07 mg kg-1) administered IV. Ponies were randomly allocated to maintenance of anaesthesia with isoflurane in oxygen (group TH; FiO2 = 0.95) or a mixture of oxygen and medical air (group TL; FiO2 = 0.65); all ponies were given a constant rate of infusion of detomidine. Animals were mechanically ventilated to maintain PaCO2 between 40 and 50 mmHg. Arterial blood gas analysis was performed every 30 minutes. The F-shunt equation was calculated for each time point T0, T30, T60 and T90. Data were analysed using linear mixed model analysis and presented as mean ± standard deviation (p < 0.05). RESULTS: PaO2 was greater in group TH than in group TL (TH: 406 ± 90, 438 ± 83, 441 ± 69 and 464 ± 53 mmHg versus TL: 202 ± 90, 186 ± 84, 172 ± 85 and 191 ± 98 mmHg at T0, T30, T60 and T90, respectively; p < 0.0001). In TH, F-shunt was < TL. Significant differences were found at T60 (TH: 13.2% ± 4.3 versus TL: 19.4% ± 8.3; p = 0.016) and T90 (TH: 11.7% ± 3.5 versus TL: 18.6% ± 9.5; p = 0.036). CONCLUSIONS AND CLINICAL RELEVANCE: Our findings do not support a beneficial effect of using a reduced FiO2 to improve oxygenation in anaesthetized and mechanically ventilated Shetland ponies.

Lung Ultrasound in Severe COVID-19 Pneumonia in the Sub-Intensive Care Unit: Beyond the Diagnostic Purpose.

Lung Ultra-Sound (LUS) can be very helpful at the diagnostic stage of COVID-19 pneumonia. We describe four clinical cases that summarize other helpful employment of LUS during the management of severe COVID-19 pneumonia with lung failure. LUS, together with clinical signs and arterial blood gases values, assists in guiding prompt clinical management of potential worsening of conditions. The monitoring of size and signs of aeration of consolidations is an important adjuvant in evaluating clinical evolution. The monitoring of LUS patterns can guide the management of non-invasive ventilation as well as the timing of CPAP weaning.

Effects of intraoperative high versus low inspiratory oxygen fraction (FiO2) on patient's outcome: A systematic review of evidence from the last 20 years.

Despite numerous studies, controversies about the best intraoperative FiO2 remain. In 2016, the World Health Organization (WHO) recommended that adult patients undergoing general anaesthesia should be ventilated intraoperatively with an 80% FiO2 to reduce surgical site infection (SSI). However, several data suggest that hyperoxia could have adverse effects. In order to determine the potential effect of FiO2 on SSI, we included in this systematic review 23 studies (among which 21 randomised controlled trials [RCT]) published between 1999 and 2020, comparing intraoperative high versus low FiO2. Results were heterogeneous but most recent studies on one hand, and the largest RCTs on the other hand, reported no difference on the incidence of SSI regarding intraoperative FiO2 during general anaesthesia. There was also no difference in the incidence of SSI depending of intraoperative FiO2 in patients receiving regional anaesthesia. The review on secondary endpoints (respiratory and cardiovascular adverse events, postoperative nausea and vomiting, postoperative length-of-stay and mortality) also failed to support the use of high FiO2. On the opposite, some data from follow-up analyses and registry studies suggested a possible negative effect of high intraoperative FiO2 on long-term outcomes. In conclusion, the systematic administration of a high intraoperative FiO2 in order to decrease SSI or improve other perioperative outcomes seems unjustified in the light of the evidence currently available in the literature.

Associations between intraoperative ventilator settings during one-lung ventilation and postoperative pulmonary complications: a prospective observational study.

BACKGROUND: The interest in perioperative lung protective ventilation has been increasing. However, optimal management during one-lung ventilation (OLV) remains undetermined, which not only includes tidal volume (VT) and positive end-expiratory pressure (PEEP) but also inspired oxygen fraction (FIO2). We aimed to investigate current practice of intraoperative ventilation during OLV, and analyze whether the intraoperative ventilator settings are associated with postoperative pulmonary complications (PPCs) after thoracic surgery. METHODS: We performed a prospective observational two-center study in Japan. Patients scheduled for thoracic surgery with OLV from April to October 2014 were eligible. We recorded ventilator settings (FIO2, VT, driving pressure (ΔP), and PEEP) and calculated the time-weighted average (TWA) of ventilator settings for the first 2 h of OLV. PPCs occurring within 7 days of thoracotomy were investigated. Associations between ventilator settings and the incidence of PPCs were examined by multivariate logistic regression. RESULTS: We analyzed perioperative information, including preoperative characteristics, ventilator settings, and details of surgery and anesthesia in 197 patients. Pressure control ventilation was utilized in most cases (92%). As an initial setting for OLV, an FIO2 of 1.0 was selected for more than 60% of all patients. Throughout OLV, the median TWA FIO2 of 0.8 (0.65-0.94), VT of 6.1 (5.3-7.0) ml/kg, ΔP of 17 (15-20) cm H2O, and PEEP of 4 (4-5) cm H2O was applied. Incidence rate of PPCs was 25.9%, and FIO2 was independently associated with the occurrence of PPCs in multivariate logistic regression. The adjusted odds ratio per FIO2 increase of 0.1 was 1.30 (95% confidence interval: 1.04-1.65, P = 0.0195). CONCLUSIONS: High FIO2 was applied to the majority of patients during OLV, whereas low VT and slight degree of PEEP were commonly used in our survey. Our findings suggested that a higher FIO2 during OLV could be associated with increased incidence of PPCs.

A snapshot of the oxygenation of mechanically ventilated patients in one Australian intensive care unit.

Hyperoxaemia in patients undergoing mechanical ventilation (MV) has been found to be an independent predictor of worse outcome and in-hospital mortality in some conditions. Data suggests that a fraction of inspired oxygen (FiO2) of 0.4 or lower may produce hyperoxaemia although it is commonly accepted without adjustment in ventilator settings. The primary aim of this study was to observe current practice at one Australian tertiary intensive care unit (ICU) with regard to prescription and titration of oxygen (O2) in patients undergoing MV, in particular whether they received higher FiO2 than required according to arterial blood gas (ABG) results, and whether there was FiO2 titration as a response to initial ABG results during the 12 hours following. A retrospective observational study of 151 ICU patients undergoing MV between November 2013 and February 2014 was conducted, with ABGs as the primary outcome measure. There were 250 ABG measures, with mean FiO2 0.38 (range 0.3-1.0) and mean PaO2 114 mmHg (standard deviation 36). Over all observations, 197 (79%) were of FiO2 ≤0.4, however no patients were ventilated on room air (FiO2 0.21) and 114 (46%) were in the hyperoxaemic range. Oxygen titration (up or down) occurred in 31% of patients. Morning ABGs were taken at a time suggested by ICU guidelines, and on review of these measures, the mean FiO2 was lower than that purported to create toxicity. Subsequently, almost one-third of the cohort had their FiO2 titrated, however there was a floor effect whereby 39%-43% of the cohort received an FiO2 of 0.3.

The effect of the inspired oxygen fraction on arterial blood oxygenation in spontaneously breathing, isoflurane anaesthetized horses: a retrospective study.

OBJECTIVES: To investigate the influence of two inspired oxygen fractions (FiO(2)) on the arterial oxygenation in horses anaesthetized with isoflurane. STUDY DESIGN: Retrospective, case-control clinical study. ANIMALS: Two hundred equine patients undergoing non-abdominal surgery (ASA class 1-2), using a standardized anaesthetic protocol and selected from anaesthetic records of a period of three years, based on pre-defined inclusion criteria. METHODS: In group O (n = 100), medical oxygen acted as carrier gas, while in group M (n = 100), a medical mixture of oxygen and air (FiO(2) 0.60) was used. Demographic data, FiO(2), arterial oxygen tension (PaO(2)) and routinely monitored physiologic data were recorded. The alveolar-arterial oxygen tension difference [P(A-a)O(2)] and PaO(2)/FiO(2) ratio were calculated. The area under the curve, standardized to the anaesthetic duration, was calculated and statistically compared between groups using t-tests or Mann-Whitney tests as appropriate. Categorical data were compared using Chi-square tests. RESULTS: No significant differences in age, body weight, sex, breed, surgical procedure, position, anaesthetic duration or arterial carbon dioxide tension were found. Mean FiO(2) was 0.78 in group O and 0.60 in group M. Compared to group O, significantly lower values for PaO(2) and for P(A-a)O(2) were found in group M. In contrast, the PaO(2)/FiO(2) ratio and the percentage of horses with a PaO(2) <100 mmHg (13.33 kPa) were comparable in both groups. CONCLUSIONS: Although a reduction of the inspired oxygen fraction resulted in a lower PaO(2), the P(A-a)O(2) was also lower and the number of horses with PaO(2) values <100 mmHg was comparable. CLINICAL RELEVANCE: In healthy isoflurane anaesthetized horses, the use of a mixture of oxygen and air as carrier gas seems acceptable, but further, prospective studies are needed to confirm whether it results in a lower degree of ventilation/perfusion mismatching.

Hemodynamics and arteriovenous malformations in cavopulmonary anastomosis: the case for residual antegrade pulsatile flow.

OBJECTIVES: Continuous flow in Fontan circulation results in impairment of pulmonary artery endothelial function, increased pulmonary vascular resistance, and, potentially, late failure of Fontan circulation. Bidirectional cavopulmonary shunt is the interim procedure in palliation of patients with single-ventricle physiology, but pulmonary arteriovenous malformations occur in many patients. In a porcine chronic model of cavopulmonary shunt, we studied pulmonary hemodynamics, pulmonary arteriovenous malformation occurrence, and gas exchange capabilities. We hypothesized that residual antegrade pulsatile pulmonary flow may attenuate the deleterious effects of nonpulsatile Fontan-type circulation. METHODS: Thirty pigs underwent a sham procedure (n = 10, group I), a cavopulmonary shunt with right pulmonary artery ligation (n = 10, group II, nonpulsatile), or a cavopulmonary shunt with proximal right pulmonary artery partial ligation (n = 10, group III, micropulsatile). Three months later, in vivo hemodynamics, blood gas exchange, pulmonary arteriovenous malformation occurrence, and lung histology were assessed. RESULTS: At 3 months, group II right lungs demonstrated significantly increased pulmonary artery pressure, pulmonary vascular resistance, and evidence of pulmonary arteriovenous malformations compared with groups I and III (all P < .001). Group III lungs also showed increased pulmonary artery pressure and pulmonary vascular resistance compared with the sham group, but significantly less than group II. Group III right lungs had the best gas exchange performance, with less histologic changes compared with group II. CONCLUSIONS: We developed a viable chronic large animal model of bidirectional cavopulmonary anastomosis. Residual antegrade pulsatile flow in the setting of a cavopulmonary shunt prevents pulmonary arteriovenous malformation formation and attenuates, but does not suppress, the development of pulmonary hypertension. From a clinical standpoint, these data would support keeping a small amount of antegrade pulsatile flow during creation of a cavopulmonary shunt.

Effects of inspired oxygen fraction in discriminating venous from arterial blood in percutaneous central venous catheterization under general anesthesia.

BACKGROUND: A low fraction of inspired oxygen (FiO(2)) increases venous deoxygenated hemoglobin concentrations, making the color of the blood darker. The present study was aimed to determine the effects of FiO(2) on the ability to discriminate venous from arterial blood. METHODS: One-hundred and sixty surgical patients undergoing percutaneous central venous access of the internal jugular vein were randomly assigned to receive an FiO(2) of 0.2, 0.4, 0.6, or 1.0 (n = 40 each) for at least 20 min prior to central line placement under general anesthesia. Vascular access was achieved with a 22-gauge needle; 2 ml of blood was withdrawn and shown to three physicians including the operator. Each of them was asked to identify the blood as 'arterial', 'venous' or 'not sure'. Simultaneous blood gas analysis of the samples was performed on blood taken from the puncture site and the artery after visual comparison to confirm blood's origin and hemodynamic measurements. RESULTS: Lowering FiO(2) progressively increased venous deoxygenated hemoglobin concentrations (2.24 ± 1.12, 3.30 ± 1.08, 3.66 ± 1.15, and 3.71 ± 1.33 g/dl) in groups having an FiO(2) of 1.0, 0.6, 0.4 and 0.2, respectively (P < 0.001), thereby facilitating the 'venous' blood identification (P < 0.001). Neither heart rate nor mean arterial pressure differed among the groups. None developed hypoxemia (percutaneous hemoglobin oxygen saturation < 90%) in any group during the study period. CONCLUSIONS: A low FiO(2) increases venous deoxygenated hemoglobin levels, thereby facilitating the recognition by clinicians of its venous origin in percutaneous central venous catheterization under general anesthesia.

Effects of inspired oxygen fraction in discriminating venous from arterial blood in percutaneous central venous catheterization under general anesthesia / 대한마취과학회지

BACKGROUND: A low fraction of inspired oxygen (FiO2) increases venous deoxygenated hemoglobin concentrations, making the color of the blood darker. The present study was aimed to determine the effects of FiO2 on the ability to discriminate venous from arterial blood. METHODS: One-hundred and sixty surgical patients undergoing percutaneous central venous access of the internal jugular vein were randomly assigned to receive an FiO2 of 0.2, 0.4, 0.6, or 1.0 (n = 40 each) for at least 20 min prior to central line placement under general anesthesia. Vascular access was achieved with a 22-gauge needle; 2 ml of blood was withdrawn and shown to three physicians including the operator. Each of them was asked to identify the blood as 'arterial', 'venous' or 'not sure'. Simultaneous blood gas analysis of the samples was performed on blood taken from the puncture site and the artery after visual comparison to confirm blood's origin and hemodynamic measurements. RESULTS: Lowering FiO2 progressively increased venous deoxygenated hemoglobin concentrations (2.24 +/- 1.12, 3.30 +/- 1.08, 3.66 +/- 1.15, and 3.71 +/- 1.33 g/dl) in groups having an FiO2 of 1.0, 0.6, 0.4 and 0.2, respectively (P < 0.001), thereby facilitating the 'venous' blood identification (P < 0.001). Neither heart rate nor mean arterial pressure differed among the groups. None developed hypoxemia (percutaneous hemoglobin oxygen saturation < 90%) in any group during the study period. CONCLUSIONS: A low FiO2 increases venous deoxygenated hemoglobin levels, thereby facilitating the recognition by clinicians of its venous origin in percutaneous central venous catheterization under general anesthesia.

Bispectral index in dogs with high intracranial pressure, anesthetized with propofol and submitted to two levels of FiO2 / Índice biespectral em cães com pressão intracraniana elevada, anestesiados com propofol e submetidos a dois níveis de FiO2

The effects of inspired oxygen fractions (FiO2) of 1 and 0.6 on bispectral index (BIS) in dogs with high intracranial pressure, submitted to a continuous rate infusion of propofol were evaluated. Eight dogs were anesthetized on two occasions, receiving, during controlled ventilation, an FiO2 = 1 (G100) or an FiO2 = 0.6 (G60). Propofol was used for induction (10mg.kg-1, IV), followed by a continuous rate infusion (0.6mg.kg-1.minute-1). After 20 minutes, a fiber-optic catheter was implanted on the surface of the right cerebral cortex to monitor the intracranial pressure, the baseline measurements of BIS values, signal quality index, suppression ratio number, electromyogram indicator, end-tidal carbon dioxide partial pressure, mean arterial pressure, intracranial pressure and cerebral perfusion pressure were taken. Then, the blood flow from the right jugular vein was interrupted in order to increase intracranial pressure and after 20 minutes additional recordings were performed at 15-minute intervals (T0, T15, T30, T45 and T60). The arterial oxygen partial pressure varied according to the changes in oxygen. For the other parameters, no significant differences were recorded. The BIS monitoring was not influenced by different FiO2.

Avaliaram-se os efeitos das frações inspiradas de oxigênio (FiO2) de 1 e 0,6 sobre o índice biespectral (BIS) em cães com pressão intracraniana elevada e submetidos a infusão contínua de propofol. Oito animais foram anestesiados em duas ocasiões, recebendo durante a ventilação controlada FiO2 = 1(G100) ou FiO2 = 0,6 (G60). Propofol foi usado para indução (10mg.kg-1) e seguido por infusão contínua (0,6mg.kg-1minuto-1). Após vinte minutos da implantação do cateter de fibra óptica do monitor de pressão intracraniana, na superfície do córtex cerebral direito, realizaram-se as mensurações basais de BIS, índice de qualidade de sinal, taxa de supressão, eletromiografia, pressão parcial de dióxido de carbono ao final da expiração, pressão arterial média, pressão intracraniana e pressão de perfusão cerebral. Em seguida, interrompeu-se o fluxo sanguíneo da veia jugular direita, para o aumento da pressão intracraniana e depois de 20 minutos, novas mensurações foram realizadas em intervalos de 15 minutos (T0, T15, T30, T45 e T60). A pressão parcial de oxigênio no sangue arterial variou conforme a FiO2. Para os outros parâmetros não foram registradas diferenças significativas. Conclui-se que o monitoramento pelo BIS não foi afetado pelo emprego de diferentes FiO2.

The influence of inspired oxygen fraction for the diagnosis of acute respiratory distress syndrome / 中华急诊医学杂志

Objective To investigate the influence of inspired oxygen fraction (FiO2) on the ratio of PaO2/FiO2(P/F) during the implementation of lung protective ventilation strategy in patients with acute respiratory distress syndrome(ARDS) in order to unravel its clinical significance. Method This was a prospective study of 16 selected patients with ARDS treated with mechanical ventilation ( MV ) to get ratio of P/F in range of 100 to 200 by PEEP≥5 cmH2O and high inspired oxygen. After lung recruitment maneuvers by BiPAP with high pressure (PH) of 40 cmH2O for40 s, the MV was maintained the basic requirement for stabilizing the patients for 30 minutes. A series of FiO2 were set at fractions of 0.5,0.6,0.7,0.8,0.9 and 1in random sequence, and the changes of respiratory mechanics, blood gas and hemodynamics under the different concentrations of FiO2 were analyzed by using SPSS version 13.0 software. Results ( 1 ) The ratio of P/F increased as FiO2 increased, and it's significant as FiO2 increased to 0.7 or above. As the fractions of FiO2 were set at 0.5 and 1. O, the ratios of P/F changed in 24.70% ± 23.36% respectively. ( 2 ) Of them,6 patients ( 37.5% ) treated with FiO2 set at 0.5 had the ratio of P/F ＜ 200, and the fraction of FiO2 was increased to 1.0, the P/F ＞ 200. (3) FiO2 and Qs/Qt were negatively correlated ( r = - 0.390, P = O. 027 ),the higher inspired oxygen fraction, the lower shunt. When the fractions of FiO2 were set at 0.5 and 1.0 ,there was a positive correlation between △Qs/Qt and △P/F( r = 0.82, P = 0.005 ). Conclusions The inspired oxygen fraction affects the ratio of P/F, which may be resulted from shunt and it may influence the diagnosis of ARDS.